Single active antenna spatial modulation with transmit diversity of orders two and three

Conventional spatial modulation (SM) offers a low-complexity multiple-input multiple-output (MIMO) transmission framework by activating a single transmit antenna per symbol interval, thereby eliminating inter-antenna synchronization requirement. However, SM is inherently unable to achieve transmit diversity. To address this limitation, this paper investigates the realization of higher order transmit diversity in SM systems where only one transmit antenna remains active at any given instance, while transmission is extended across two or three time slots. Specifically, we derive design criteria for second and third order transmit diversity in single active antenna SM systems when utilizing two or three time slots. Based on the obtained criteria, designs for more than one time slot are proposed that achieve higher diversity order for the maximum likelihood (ML) receiver. Unlike the conventional SM, the proposed schemes do not require the number of transmit antennas to be an integer power of two. Furthermore, we develop a low complexity coherent ML detector for the presented designs. The results show that the introduced schemes outperform previous approaches.